Why is it that for well over the last 100 years there has been a near even split between the two parties?

Why is it that for well over the last 100 years there has been a near even split between the two parties?

Over time, I would think there would develop a consensus of opinion amongst the American public. However, that has not happened.

Why is it that for well over the last 100 years there has been a near even split between the two parties?
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